1. Field of the Invention
This application relates to electromagnetic filters, and in particular, to compact planar microwave blocking filters.
2. Background
Cryogenic electronics systems may contain low-noise devices such as Josephson tunnel junctions, coulomb blockade devices, and bolometric detectors. Microwave thermal blocking filters may be utilized in the cryogenic electronics systems to realize isolation between cooled elements of the low-noise devices and room temperature readout and bias electronics. The use of thermal blocking filters may prevent degradation of the detector performance from Johnson noise emitted at warmer elements of electronics required by the sensor system.
Providing a low-noise DC bias line to the detectors is possible using a large value shunt capacitor. However, realizing this function with a broadband readout capability is challenging. A dissipative conventional approach includes utilizing a resistor loaded filter. In this approach, microwave power is absorbed along the filter structure to provide broadband attenuation. However, to provide sufficient attenuation at high frequency, the resister loaded filter requires a long line, which in turn creates a large capacitance and limits the operating bandwidth of the signal. Additionally, this approach requires the use of lossy, or loaded, dielectric materials, which are not compatible with thin film fabrication processes. A non-dissipative approach may be effective at blocking thermal noise power, however, the approach must adequately address spurious transmission resonances and sensitivity to impedance matching.
Thus, it may be beneficial to provide microwave thermal blocking filters which overcome these problems.